This invention relates generally to golf clubs and more particularly to the assembly of golf club heads to golf club shafts.
A critical step in the manufacture of golf clubs is the assembly of the club head to the club shaft. Typically, to achieve a suitably secure bond between the club head and the shaft, an epoxy adhesive is applied to the shaft and/or the hosel bore. The shaft is then inserted into the hosel bore and the adhesive on the joint is allowed to cure. Since the alignment between the longitudinal axis of the golf club shaft and the club head is critical, various methods and apparatus have been proposed for maintaining the alignment between the club shaft and the club head while the adhesive is curing.
U.S. Pat. No. 5,771,552 to Karner, et al. discloses an apparatus comprising a plurality of clamps used to hold the club head and shaft in alignment. A heat-activated epoxy is applied to the joint, which is thereafter heated by means of an inductive heating element. A separate cold air cooling member returns the golf club joint to an operator handleable temperature for speed of production. Disadvantages of the foregoing method include the requirement for specialized heat activated bonding agents and the necessity of a complicated fixture. U.S. Pat. No. 4,597,577 discloses a golf club assembly system in which the golf club shaft is retained in the hosel bore by means of a pin-and-slot fastener that may be used with or without a conventional adhesive. Disadvantages of the aforementioned assembly may include the cost of manufacturing the slot in the shaft tip as well as the need for a precisely located pin transversely mounted within the hosel bore.
In yet another prior art assembly method, the bottom of the hosel bore is designed to create an interference fit with the shaft tip. The friction between the shaft tip and the bottom of the hosel bore holds the shaft in place as the adhesive cures. Although this method provides excellent alignment between the club head and shaft without complicated alignment fixtures or expensive custom shaft arrangements, it does have one drawback. Normal manufacturing tolerances of +/−0.003 on the shaft and the hosel bore turn a nominal 0.001 inch interference fit into a theoretical fit of from 0.007 inch of interference to 0.005 inch of clearance. The statistical distribution about the minimum and maximum tolerances improves yield over the print tolerances, however, manufacturing tolerances do create a not-insignificant number of clubs that are rejected because either the interference is too great for the shaft to be assembled to the club or there is unacceptable clearance between the shaft and the hosel bore. Reducing the tolerances and/or selectively fitting maximum material shafts to minimum material bores and vice versa improves yield, however, there is a cost associated with these manufacturing techniques. What is needed then is a method of assembling a golf club shaft to a club head that provides an interference fit at the base of the hosel bore without the need to tightly control tolerances or selectively fit shafts to match hosel bores.